The present invention relates generally to a seat belt system, and more particularly, to a seat belt system constructed to restrain upon vehicular collision a passenger with tension of a webbing alleviated after preventing tightening thereof by a retractor.
A seat belt system is disclosed, for example, in JP-U 63-74358. Referring to FIG. 13, with this seat belt system, when a collision sensor 101 detects a vehicular collision, an actuating rod 103 of a pusher 102 draws a webbing 107 between a spool 108 of a retractor 104 and a shoulder anchor 106, preventing tightening of the webbing 107 by the retractor 104. After maximum operation of the actuating rod 103, drawing force thereof is gradually decreased to alleviate tension of the webbing 107.
With the above prior art, however, the webbing 107 does not have a specified drawing load, retraction amount, and tension alleviating timing after retraction by the pusher 102. As a result, if the webbing 107 has small retraction amount by the pusher 102, a tightening amount of the webbing 107 by the retractor 104 or slack amount thereof cannot sufficiently be absorbed. On the other hand, if the tension alleviating timing is lagged due to great retraction amount or retraction load of the webbing 107 by the pusher 102, restraint force to a passenger becomes much too great.
Further, a means for alleviating tension of the webbing 107 is constructed to rely upon the balance between a return amount of the actuating rod 103 from the pusher 102 due to degassing and the tightening amount of the webbing 107 by the retractor 104, so that even if the webbing 107 has appropriate retraction amount, retraction load, and tension alleviating timing by the pusher 102, the webbing 107 is difficult to stably draw out from the retractor 104 with a predetermined load. Furthermore, when drawing force of the actuating rod 103 for the webbing 107 is suddenly decreased due to sudden degassing of the pusher 102, the retractor 104 cannot carry out tightening of the webbing 107 in a manner to follow that decrease in drawing force, resulting in difficult slackness of the webbing 107.
On the other hand, even if the prior art webbing 107 is of the type having a fuse characteristic that when arriving at a fuse load as previously set, elongation is made by a predetermined amount so as to enable restraint on a load increase, there arises the problem that when the tension alleviating timing is lagged due to great retraction amount or retraction load of the webbing 107 by the pusher 102, the pusher 102 absorbs the predetermined amount of elongation of the webbing 107 by the fuse characteristic, resulting in difficult application of the fuse characteristic upon vehicular collision.
It is, therefore, an object of the present invention to provide a seat belt system having an improved performance.